Is there any standard heating temperature for sealed type bearing when put in a bearing heater?

Our plant mechanic experienced grease degradation (Oil separation from grease base material) of sealed bearing when he put it in the bearing heater with 115 deg C in preparation for motor bearing installation.

I read an article (see attached) from William H. Detweiler, SKF USA Inc., King of Prussia, PA, that Normal motor bearing operating temperatures range from 140°F (60°C) to 160°F (71°C). We use this temperature range as our guide in monitoring and trending motor bearings.

But how about if we put it in the bearing heater with applied temp of 100°C or more for easy installation?

Is there any standard temperature setting in the bearing heater (especially if sealed type bearings are heated)?

Is it proper way to put the sealed type bearing into the bearing heater for easy installation?

Dear Reggie,

Typically you want to expand the bearing just enough to allow a quick install onto the shaft. Our experience has been to probe the bearing temperature as you are heating the bearing. Once the bearing has reached no higher than 250°F (121°C) remove the heat source and quickly install the bearing. Our experience has also been with rod type heaters and not a full emersion oven. Not to condemn the grease you're using, but those temperatures should not be affecting the separation. Check a few things - amount of grease in bearing AND shelf time bearing and grease have seen prior to this operation. If this is something new and your proceedure has been performed prior to this with a similar installation, make note and continue as normal. This may be a single case incident due to improper lubrication level.

If this is something new and your proceedure has been performed prior to this with a similar installation, make note and continue as normal. This may be a single case incident due to improper lubrication level.[/QUOTE]


Thanks Shaun, yes, this is the first time that happen to us..thats why i was doubful if our procedure were correct...at least now, you give me an idea...hope this will be rare cases and would not happen again...thank you so much!

Reggie,

Shawn is correct in stating that a normal quality grease should not be impacted by the temperatures you reported for your installation. Grease dropping point is the temperature when the oil will separate from the grease in a liquid form. Most normal application greases have much higher dropping points. For example, Mobilith AW, a common lithium bearing grease, has a dropping point of 260 deg C.

Hope that helps.

Rich Wurzbach
MRG Power Labs
MRG Power Labs
Maintenance Reliability Group, LLC

SKF recommends 125C limit during mounting of cylindrical bore bearings for dimensional stability, but further limits temperature to 80C for mounting of shielded bearings.

I agree that grease degradation shouldn't be a concern for short times at this temperature with most greases. Maybe the basis for SKF's 80C limit has to do with thermal expansion damaging the shields? I'm not sure... we certainly have a few shielded bearing applications that exceed 80C during operation at the bearing (in fact close to 80C on the housing).

http://www.skf.com/portal/skf/home/products?paf_dm=shar...g=en&newlink=1_0_136

quote:

It is generally not possible to mount larger bearings in the cold state, as the force required to mount a bearing increases very considerably with increasing bearing size. The bearings, the inner rings or the housings (e.g. hubs) are therefore heated prior to mounting.

The requisite difference in temperature between the bearing ring and shaft or housing depends on the degree of interference and the diameter of the bearing seating. Bearings should not be heated to more than 125 °C as otherwise dimensional changes caused by alterations in the structure of the bearing material may occur. Bearings fitted with shields or seals should not be heated above 80 °C because of their grease fill or seal material.

When heating bearings, local overheating must be avoided. To heat bearings evenly, SKF electric induction heaters (fig 8) are recommended. If hotplates are used, the bearing must be turned over a number of times. Hotplates should not be used for heating sealed bearings.

Or maybe SKF is just being overly-conservative to cover all possible types of grease... and further using a continuous temperature limit even though this will be only a brief time?

We routinely heat grease-filled bearings to 220F (105C) during installation and there have been no adverse effects that I know of.

I came up with a bearing heating guidance at my plant because bearings were routinely being overheated. I went with SKF's recommendations for maximum temperature on shielded and sealed bearings but I don't see why they wouldn't be okay heated to 120C as stated above. Maybe the temperature was measured in the wrong place, outer race instead of inner race?
I've attached a copy of the guidance I came up with.

Ed

ER010717R301_Bearing-Heating.pdf (155 Kb, 45 downloads) bearing heating

Ed - what kinds of problems did you see from overheating the bearings during mounting? Was it immediately evident?

What were you using as a temperature limit before, and how were you heating (induction heater or other)

(just curious)

Or maybe I just misunderstood the comment. When you said bearings were routinely being overheated, did you simply mean that you routinely exceeded the 80C recommended by SKF and other manufacturers?

Pete,
Sorry I'm so late with this reply... I forgot to check this post.
What we saw from the overheating was shortened bearing life. We had some bearings start degrading 6 months after installation and we had had several "premature" failures in the past few years. I was observing the installation of the new bearings and discovered that they were being heated to 300 or more degrees (F) "because the hotter they are the easier they go on". Our maintenance guys had no idea that there was a maximum temperature for heating. An induction heater was used. I came up with the heating guidance and did some training. We also threw out all of the old induction heaters that just have an on-off switch and bought new models with the thermocouple, temperature read-out and demagnetization built in. A lot of people don't know that when using those old induction heaters (the ones with just a switch), that you are supposed to remove the bar after heating the bearing and wave the bearing between the posts to de-magnetize it....
After creating the guidance and doing the training, we have had much longer average bearing life.